The present invention relates to a method and it's a device used to observe a specimen using a SEM (Scanning Electron Microscope) in the observance or measurement of a semiconductor wafer, etc in a process of semiconductor manufacture.
It is getting harder to control front-end semiconductor processing as a result of the increasing miniaturization of semiconductors. Subtle changes in pattern shapes, such as corner radiuses, as well as the heights, line widths, and sidewall gradient angles of the patterns of the semiconductors, make a significant impact on the electrical characteristics of semiconductor patterns. Therefore, a technology to detect the changes in a process and control a process by measuring the dimensions or shapes of a semiconductor during manufacture is needed. A technology to estimate a 3D profile from the observations of sidewalls or images obtained by an SEM (referred to as an “SEM image” hereinafter) of a semiconductor pattern is expected to effectively control a process. It is supposed that utilizing the information of the SEM images of a specimen observed in an oblique direction will be effective for observing the sidewalls or estimating 3D profiles.
The methods to obtain such SEM images observed in an oblique direction include, for example, a method to take a tilted image by deflecting an electron beam that is irradiated from an electron optical system and tilting the direction thereof so as to. irradiate the electron beam to an object of an observation, as described in the Japanese Published Unexamined Patent Application (abbreviated to JP-A, hereinafter) No. 2000-348658; a method to take an image by tilting the stage itself which is used to move a semiconductor wafer so that any given position of a semiconductor wafer can be observed by the SEM; and a method to tilt mechanically an electron optical system of the SEM itself.
However, it is expected that the direction of observation (or the incident direction) of an observed image actually obtained using conventional technologies may have some errors relative to the set values. Therefore, the error portion may affect the analysis of the observed image afterward. For example, an error in the direction of an observation becomes an issue because dimensional values are changed by the direction of an observation when detecting a process change by monitoring dimensions, such as line widths and contact hole diameters (see “Characterization of 193 nm Resist Layers by CD-SEM Sidewall Imaging”, Proceedings of SPIE Vol. 5038, pp. 892-900, 2003). In the 3D profile reconstruction technology used for performing stereo measurement with images observed from multiple directions, the errors in the observational directions affect the errors of profiles estimated because profiles are estimated based on the observational directions of multiple SEM images and the disparities among multiple SEM images.